A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may for example project a pattern from a patterning device (e.g. a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate.
The wavelength of radiation used by a lithographic apparatus to project a pattern onto a substrate determines the minimum size of features which can be formed on that substrate. A lithographic apparatus which uses EUV radiation, being electromagnetic radiation having a wavelength within the range 5-20 nm, may be used to form smaller features on a substrate than a conventional lithographic apparatus (which may for example use electromagnetic radiation with a wavelength of 193 nm).
It is desirable to produce EUV radiation sources with increased power to increase throughput of EUV lithography. However, use of some EUV radiation sources may generate radiation with a power in excess of that which can be used effectively at the substrate. It is therefore also desirable to produce EUV radiation that can be used effectively at the substrate.
It is an object of at least one embodiment of the present invention to obviate or mitigate at least one of the problems identified above.